Silicon, Germanium Substrate Rare Earth Metal-oxide Thin Film On The Molecular Beam Epitaxial Growth, Structure And Physical Characteristics

The recent research interest towards high K materials stems from the need to replace SiO2 in metal oxide semiconductor filed effect transistors (MOSFET). Rare-earth oxides are one of the promising candidates as a suitable gate dielectric layer in MOS device materials. This thesis focuses on the growth, microstructure and physical properties of Tm2O3 films on Si (001) substrates and Er2O3 films on Ge (001) substrates.Chapter 1 and chapter 2 introduce the research backgrounds and experimental equipments & characterization methods, respectively.Chapter 3 deals with the growth and electrical properties of single crystalline Tm2O3 films on Si (001) substrates. Single crystalline Tm2O3 film is grown on Si (001) surface successfully by multi-step growth method for the first time. During growth, the substrate is kept at 600℃and the atomic oxygen partial pressure is 2 X 10"7 Torr. The SiOx interface layer formed at the early growth stage is removed by annealing at high temperature in ultra-high vacuum (UHV). The epitaxial relationship between the Tm2O3 films and the Si substrates is Tm2O3 (110)//Si (001), Tm2O3 [001]//Si [110] or Tm2O3 [1-10]//Si [110], same as that of Er2O3 and Y2O3 grown epitaxially on Si (001). Higher oxygen pressure would change the preferential growth orientations from (110) to (111) with the growth mode from epitaxy to non-epitaxy. The preferential growth orientation change is attributed to the minimization of the surface energy. After post-annealing in O2 at 450℃, the single crystalline films exhibit a dielectric constant of 10.8 and a leakage current density of 2×10-3 A/cm2 at an electric field of 1 MV cm-1 with an equivalent oxide thickness of 2.3 nm. Small angle XRR results show that the electron density of the film increases significantly after annealing, which is explained by the compensation of oxygen in the annealed films. The improvement in the electrical properties of the annealed films is also attributed to this effect. The annealing temperature effect on the electrical properties of the Tm2O3 film is also investigated. Changes of the toal capacitance value in the accumulation region after annealing at different temperatures are due to the changes of the interface layer.In chapter 4, the growth and electrical properties of amorphous Tm2O3 films on Si (001) are investigated. Amorphous Tm2O3 film with good thermal stability is fabricated. During growth, the substrate is kept at room temperature and the oxygen partial pressure is 3×10-6 Torr. In order to reduce the thickness of the interface layer, the as-deposited Tm2O3 film is annealed at high temperature in UHV. The as-deposited film is amorphous with a 1.9 nm thick SiOx interface layer. After in situ annealing at 700℃, the film still remains amorphous and the interface layer almost disappears. The absence of the interface layer after annealing is due to the reaction between the oxygen deficient TmOx and SiOx, forming Tm2O3 and Si. The K value of the amorphous Tm2O3 film after in situ annealing in UHV and post annealing in O2 ambience is 8.4 and the corresponding EOT is 2.3 nm.Compared with those in Si substrate, the carrier motilities in Ge substrate are much higher. In chapter 5, we attempt to grow high K material on Ge (001) substrate. It is found that the growth temperature has a great influence on the growth and electrical properties of the Er2O3 film grown on Ge substrate. The film deposited at room temperature is composed of an Er2O3 layer and an ErGexOy interface layer with a thickness of 5.5 nm; The film grown at 300℃has a mixed structure of Er2O3 and ErGexOy and the thickness was found to be reduced to 2.2 nm; The film grown at 450℃becomes much rougher with voids formed underneath the film, having a mixed structure of three compounds of Er2O3, GeO and ErGexOy. The growth processes of the films at different temperatures are suggested. Current images obtained by tunneling atomic force microscopy show that the film grown at 450℃has much more leaky spots than those grown at RT and 300℃, which may arise from the formation of volatile GeO in the film.Chapter 6 mainly discusses the band gap of Er2O3 film and the band offsets between Er2O3 and Ge substrate. The band gap of Er2O3 film is found to be 5.96 eV, the conduction and valance band offsets of Er2O3 to Si are 2.13 and 3.16 eV, respectively.Chapter 7 explores the passivation of the Ge substrate. Two passivation methods are attempted:ozone oxidization and Si layer passivation. However, the electrical properties of the films are not improved after passivation. Further work is needed to achieve good electrical results.